Until now, scientists have thought the cultivated rockmelon (Cucumis melo) originated in Africa because morphological studies suggested the closest relative was there, says team member, biologist Ian Telford, of the University of New England.

But Telford and colleagues have now found previously overlooked species of melons in Australia and around the Indian Ocean, which are genetically more similar to rockmelon than the African melons.

"Morphology has led us astray so often," says Telford.

Rockmelon sister species

Telford and colleagues used DNA sequence data to compare some 100 melons and cucumbers across the world.

The researchers found seven new species of cucumis in Australia, including a wild melon C. picrocarpus, widespread throughout the tropics and sub-tropics.

Surprisingly, this "sister species" turns out to be the most genetically similar to our cultivated rockmelon, says Telford.

He says C. picrocarpus would have diverged from C. melo about 3 million years ago and its ancestor would have come from Asia.

Telford and colleagues also found evidence confirming suspicions that the cucumber originated in Asia.

"There are many more wild relatives of cucumber than were suspected, particularly in Australia," says Telford, who found six new wild cucumbers.

Together with the rockmelon, the cucumber is most likely to have originated from the Himalayan region, the researchers say.

Genetic resources

Telford says the discovery of so many extra species of melon and cucumber in Asia and Australia is a boon for plant breeders.

"We now have genetic resources we didn't know about because we have all these other species," he says.

"For plant breeders, these wild populations may have traits that can be transferred to the cultivated plants."

Telford says rockmelons and cucumbers are prone to viral and fungal diseases and plant breeders have been looking to African plants to try to improve the cultivated fruit.

Unfortunately this strategy hasn't been working, because the African fruit are so genetically different, he says.